In general, orthopaedic implants can be broken down into two rather broad classifications, i.e. cemented and non-cemented. A cemented implant is one that is specifically designed to be held in contact with a bone by a layer of cement. U.S. Pat. No. 3,228,393 illustrates an implant intended for cemented use. A non-cemented implant, as defined here, is one that is specifically designed to have an initial fixation such as a press fit and a long term fixation such as bone growth into a portion of the implant. U.S. Pat. No. 3,906,550 illustrates an implant intended for non-cemented use. A non-cemented implant or press-fit implant is generally provided with some type of porous outer coating to promote bone growth about the implant and bone interdigitation within the porous structure. Two well-known porous surfaces for use as a porous surface are a wire mesh pad or a layer(s) of metal beads.
The choice between using a cemented or non-cemented implant is a decision left to the orthopaedic surgeon. In general there are several factors affecting the decision such as patient age, patient activity, and the quality of the bone stock as determined by X-rays. These factors are presented here merely as an example; in practice, many other factors may play into the surgeon's choice between a cemented of non-cemented application.
Many of the factors affecting the decision may be based primarily on X-rays or other radiographic imaging data, each of which have inherent limitations. Therefore, until the surgeon actually exposes the bone which will accept the implant, a degree of uncertainty may exist.
It is conceivable that a surgeon who originally decided on a cemented implant may, after exposing the bone, determine that a non-cemented implant would be better for the patient. The problem is that with the prior art implants, if the alternative non-cemented implant is not available, the surgeon may have no choice but to continue with the procedure and implant a less than optimal implant. To compensate for this eventuality, a surgeon could request the hospital to have in inventory and on hand during surgery both types of implants.